It is well recognized that deterioration of perishable foods can be inhibited if the foods are stored in containers from which air has been evacuated. Preservation of many substances other than foods can also be enhanced by vacuum packing. Photographic film negatives and silver objects are typical examples.
Vacuum packing of foods in processing plants is usually accomplished with complex and expensive machinery that is not practical for use in smaller scale operations. In restaurants and in the home, for example, relatively small quantities of foods are stored for consumption at a later date. The foods can be maintained in a fresher condition and the storage period can be prolonged by using evacuated containers including in instances where the stored foods are refrigerated.
A variety of container sealing devices have heretofore been developed for the purpose of enabling sealing and evacuation of containers. These have not proven to be entirely satisfactory for several reasons. Such devices typically include a container lid having an air passage and some form of valve for enabling withdrawal of air through the passage and subsequent closure and sealing of the passage. Some of these prior systems require an undesirably complicated and costly valve mechanism. Some are usable only with a particular form of specialized container. Others may be difficult to re-open when the contents of the container are to be recovered.
The more economical prior devices of this kind have a closure member at the air passage of the container lid that is typically of one of three kinds which are a plug that fits into the passage, a spherical ball check valve element or a flat piece of material that overlays the passage and a portion of the adjacent area of the lid. An inverted cup, coupled to a vacuum pump, is temporarily placed over the passage and the closure lifts to enable an outflow of air through the passage. When the vacuum source is deactivated, external air pressure acts against the closure member in a manner which seals the passage.
Each of the above discussed forms of closure member is subject to problems. Both plugs and spherical ball closures require that the passage in which they seat be formed very precisely or leakage will occur. Thin flat members that overlay the passage are subject to the same problem since it is only the portion of the member that is immediately over the passage that experiences a net downward force from ambient air pressure after the container is evacuated. Consequently, the peripheral portions of such a member that are not directly over the passage tend to be flexed upwardly and are out of contact with the surface of the lid. These upwardly flexed portions limit the zone of sealing contact to the edge of the passage and are also susceptible to being snagged and dislodged by movements in the vicinity of the container lid. In general, each of these three forms of passage closure have been less reliable than would be desirable and leakage has been a common problem.
The present invention is directed to overcoming one or more of the problems discussed above.